The Object.unobserve() method was used to remove observers set by Object.observe(), but has been deprecated and removed from Browsers. You can use the more general Proxy object instead.
The valueOf() method returns the primitive value of the specified object.
The watch() method watches for a property to be assigned a value and runs a function when that occurs.
The RangeError object indicates an error when a value is not in the set or range of allowed values.
JavaScript is designed on a simple object-based paradigm. An object is a collection of properties, and a property is an association between a name (or key) and a value. A property's value can be a function, in which case the property is known as a method. In addition to objects that are predefined in the browser, you can define your own objects. This chapter describes how to use objects, properties, functions, and methods, and how to create your own objects.
Starting with ECMAScript 2015 (ES6), a shorter syntax for method definitions on objects initializers is introduced. It is a shorthand for a function assigned to the method's name.
The __defineGetter__ method binds an object's property to a function to be called when that property is looked up.
The __defineSetter__ method binds an object's property to a function to be called when an attempt is made to set that property.
The __lookupGetter__ method returns the function bound as a getter to the specified property.
The __lookupSetter__ method returns the function bound as a setter to the specified property.
The __count__ property used to store the count of enumerable properties on the object, but it has been removed.
The Object.defineProperty() method defines a new property directly on an object, or modifies an existing property on an object, and returns the object.
The Object.entries() method returns an array of a given object's own enumerable property [key, value] pairs, in the same order as that provided by a for...in loop (the difference being that a for-in loop enumerates properties in the prototype chain as well).
The Object.isExtensible() method determines if an object is extensible (whether it can have new properties added to it).
The Object.isFrozen() determines if an object is frozen.
The Object.isSealed() method determines if an object is sealed.
The Object.keys() method returns an array of a given object's own enumerable properties, in the same order as that provided by a for...in loop (the difference being that a for-in loop enumerates properties in the prototype chain as well).
The __noSuchMethod__ property used to reference a function to be executed when a non-existent method is called on an object, but this function is no longer available.
The __parent__ property used to point to an object's context, but it has been removed.
The Object.preventExtensions() method prevents new properties from ever being added to an object (i.e. prevents future extensions to the object).